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Converting a SECAM Atari 2600 to PAL or NTSC

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Hi,

As you (may) know, the SECAM version of the Atari 2600 can only display 8 colours (based on the eight levels of grey of the B/W mode).

Depending of the revision, the console host either a NTSC TIA or a PAL TIA.

My idea was too simply revert it back to NTSC (128 colours) or PAL (104 colours).

I will try to described what I've achieved so far (note: I've made the same modifications on boths NTSC and PAL based SECAM consoles):

 

1) Pin 21 (PB3) of the 6532 (RIOT) is grounded on the SECAM model. So I lifted that pin and connected it to a simple switch (closed = to ground, open = floating) => I didn't notice any change in the video (through RF) either in B/W or COLOUR mode.

 

2) To get rid of all the additional circuitry in the SECAM model I lifted pins 2/5/6/7/8/9 (CSYNC/LUM1/BLK/LUM2/LUM0/COLOR) of the TIA for the NTSC based model and pins 2/5/6/7/9 (CSYNC/LUM1/LUM2/LUM0/COLOR) for the PAL based model. Then I built the exactly same circuit you can find in schematics to create composite signal and I added a small signal amplifier at the end.

mini_153963Capture.jpg

In both cases I got a clear B/W composite image but no colours...

 

3) I noticed the DEL pin (colour delay) is connected to +5V on the SECAM model (through a resistor). Again I lifted that pin and wired the missing part of the circuit:

mini_445056Capture.jpg

Still no colours...

 

4) Then I swapped crystals from 2 working original NTSC and PAL consoles because I thought there was an issue in frequencies used to encode the colour signal. I obviously installed the crystals from the original NTSC machine in my NTSC based SECAM console and same for PAL => Still no colours in both cases... (But still a good B/W image without rolling, probably because my TVs are all multi-standard).

 

5) Finally I lifted the same pins mentioned in 2) and 3) on both the original NTSC and PAL machines (after installing the crystals back) and installed my homemade boards in them. => I got colours. So my circuit is working.

 

I did the same tests on 3 different TVs I use for video games with no issue at all with PAL or NTSC machines connected via composite.

Now I would like to understand what is the subtle difference I missed that prevent me of getting colours on my modified SECAM machines...

If anyone has a clue he's most welcomed!

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The NTSC schematics here on AA seem to have errors in the color delay part of thecircuit.
Try this one instead (it's from the official Atari 2600 Field service manual pdf).
post-10599-0-54734600-1446480203_thumb.jpg

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The NTSC schematics here on AA seem to have errors in the color delay part of thecircuit.

Try this one instead (it's from the official Atari 2600 Field service manual pdf).

Thanks for the help. Will try that.

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sounds like a NTSC/PAL system in BW mode. Sorry that I'm too lazy to look it up right now, but are you sure the BW mode is not hotwired?

SECAM doesn't have a BW mode so this setting must have a default.

 

EDIT:

I think it is pin 21 on the 6532, this should not be grounded as this would result in BW mode.

This was your first test, but maybe you forgot to test this again when you got the other stuff working.

Normaly there is a capacitor of .01 between this leg and the ground. Check the image for a better idea where to put it.

 

post-37130-0-46756300-1446857367_thumb.png

Edited by DrWho198

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sounds like a NTSC/PAL system in BW mode. Sorry that I'm too lazy to look it up right now, but are you sure the BW mode is not hotwired?

SECAM doesn't have a BW mode so this setting must have a default.

 

EDIT:

I think it is pin 21 on the 6532, this should not be grounded as this would result in BW mode.

This was your first test, but maybe you forgot to test this again when you got the other stuff working.

Normaly there is a capacitor of .01 between this leg and the ground. Check the image for a better idea where to put it.

 

attachicon.gifBW-COL.png

 

Yeah that's the first thing I did:

 

 

1) Pin 21 (PB3) of the 6532 (RIOT) is grounded on the SECAM model. So I lifted that pin and connected it to a simple switch (closed = to ground, open = floating) => I didn't notice any change in the video (through RF) either in B/W or COLOUR mode.

 

I don't think the capacitor is necessary (not present in my NTSC model) but I wired it anyway with no changes.

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Why not come up with an external device to do this conversion? In the future the SECAM model might become very $$$$. Isn't SECAM totally phased out yet?

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External? If you mean hooking something up between the secam atari and a NTSC tv then you can scratch this option. There is no way ti get NTSC colors out of a PAL or SECAM atari.

 

For people who wonder why someone does not just buy a NTSC atari instead of looking at the option to mod one, I'll give you a short explanation.

 

1) Although a NTSC atari can be baught cheap from the US, shipping it to europe costs you a lot of money. Once you import it you have to pay even more as taxes are calculated on the value of the object+shipping.

2) It is interesting to see what is the essential difference between different region consoles.

 

I have a NTSC atari, but it did not come cheap.

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There is no way ti get NTSC colors out of a PAL or SECAM atari.

Actually I think that's possible :

If you take the TIA and the crystals from a NTSC console and install them into a PAL console it should work as a NTSC console. But you need a NTSC TIA.

Converting a SECAM console to either PAL or NTSC seems easier to me as some SECAM consoles are based on the PAL TIA, others on the NTSC TIA.

Architecture is pretty similar and I didn't think It could be so complicated. I've already made a lot of test but I'm sure I'm missing something.

Something a video expert could solve I guess.

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Ok It's almost here!

So I had no success in converting a REV2 board (based on a NTSC TIA) from SECAM to NTSC.

I had no success in converting a REV14 board (based on a PAL TIA) from SECAM to PAL.

Now I've installed my circuit in a REV7 board (based on a PAL TIA) and obtained different colours than the original ones!

But... Some are wrong. For example in Kangaroo, background is orange (instead of blue) and sides are green (instead of brown)...

Surprisingly strawberries are pink and the score is yellow, which is normal. So It's not a complete colour swap.

Although It seems to be a small step forward, I'm even more lost than before as I used the same circuit...

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wow... how... how many secams do you have? I wich I had one for my collection... but I can't find any at a decent price in belgium or france.

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wow... how... how many secams do you have? I wich I had one for my collection... but I can't find any at a decent price in belgium or france.

Probably 10 or more (I've moved to a foreign country, have lost a part of my collection and few days ago I found a box I didn't open yet full of 2600s). Where do you live? Perhaps you can send me a NTSC or PAL console and I can send you a SECAM console.

Do you have any SECAM compatible TV?

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Hi there.

 

I'm very interested by your researches as I also think it IS possible to get an ATARI 2600 PAL from a SECAM one. I got 5 Atari 2600 SECAM and I'd really like to grab all the colors from them.

Is your project in stand by or did you finaly had a solution to archieve this ?

 

 

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Posted (edited)

I restored schematic for my Atari 2600 Junior (PAL) and Video Computer System (SECAM) and looks like you're missing points 2 and 4. Here is a complete list of things you have to do in order for succesful SECAM to PAL modification with images how PCB needs to be modified (there are ale different Atari Secam PCBs so I can't guarant this will work for different models):

Atari 2600 Junior (PAL/NTSC, depending of the wiring):
4585182000_1615460424_thumb.jpg 3704738400_1615460426_thumb.jpg 8034179200_1615460423_thumb.jpg

Video Computer System (SECAM):
5297969300_1615460267_thumb.jpg 8692104200_1615460269_thumb.jpg 8229953300_1615460264_thumb.jpg


1) Replace crystals

                 SECAM        PAL
TIA pin 11 | 3.562500 MHz | 3.546894 MHz
TIA pin 12 | 4.453125 MHz | 4.433618 MHz
TIA pin 8  | GND          | 0.8867236 MHz

SECAM model uses 3.562500MHz (Y200) and 4.453125MHz (Y202) while the PAL one uses 3.546894MHz and 4.433618MHz (the ratio for both models is the same: 4.453125 / 3.562500 = 1.25).
While the 4.433618MHz is common PAL crystal and thus easy to find, 3.546894MHz is hard (impossible?). Luckily, you can easily find 4 * 3.546894 MHz = 14.187576 MHz and then divide output frequency by 4 and fed it into TIA pin 11. You use additional 74*74 for division by 4:
5193754000_1615455072.png

Unfortunatelly, for unknown reasons, when you use the existing SECAM model's generator and just replace 3.562500 with 14.187576, you get 14.1826MHz and after division 3.54565 which is too far from 3.546894. I have no idea if this is because the SECAM model's two transistor common base + common emitter generator is not suited for such fast crystals and some R/C/transistors needs to be changed.
5035275800_1615455324_thumb.jpg

The solution is to ignore the existing generator by disconnecting it from TIA's pin 11 and build new one. This one will do the trick:
6757877300_1615455616_thumb.jpg

Here is how you can disconnect the old generator and where to connect output of the new one:
3990648900_1615456509_thumb.jpg

2) Pull-up TIA pin 9 (color) to +5V by 1k resistor
This pin is is open collector, but is not wired to anything in SECAM model, that why you need to pull it up and then wire later to your amplifier board
4904071900_1615457002_thumb.jpg

3) Disconnect TIA pin 10 (CADJ) from +5V and connect it to potentiometer.
This pin sets the color delay. In PAL model it is connected to the following circuit, allowing voltage adjustment from 0V to around 6.4V.
8229417700_1615457124_thumb.jpg
From my observation, the voltage that sets proper delay is around 3.37V so you don't need the +9V and diode clamping part. Value of potentiometer is not critical, you can add any. Just don't forget about the cap which filters the voltage. You should put the capacitor outside the metal shielding so you can change the voltage later after enclosing the shields.
6402038000_1615457781_thumb.jpg

4) Disconnect TIA pin 8 from GND and connect it to 0.8867236 MHz.
In PAL model, 4.433618 MHz crystal clocks TIA pin 12 and then an inductor is used to filter out the basic and third harmonics, so that the fifth harmonics (4.433618 / 5 = 0.8867236 MHz) is fed into TIA pin 8.
6875883400_1615458662_thumb.jpg

SECAM model has pin 8 tied to GND. Luckily, the whole generator is the same so all you have to do is to connect the collector of NPN transistor with TIA pin 8 through 100R resistor.
Disconnecting pin 8 from GND needs two cuts and one wire as shown below:
6126225700_1615459379_thumb.jpg

5) COLOR/BW switch
Disconnect 6532's pin 21 from GND and connect it either to +5V (for permanent COLOR mode) or to the middle of of BW/COLOR switch (for switching capability). Be awared that BW/COLOR switch in SECAM model is wired differently than in PAL/NTSC, resulting in opposite behaviour:
* switch slided to the top = GND applid to this pin = BW mode,
* switch slided to the bottom = +5V applied to this pin = color mode
9094460100_1615459736_thumb.jpg

6) Amplifier board
From my experience, the best video is achieved by separating luma from chroma (S-VIDEO mode). The following amplified board can be used for that purpose:
3089783700_1615459812_thumb.jpg 8246957600_1615459819_thumb.jpg 7975428500_1615459830_thumb.jpg

Final:
7240515200_1615460136_thumb.jpg  2382119600_1615460135_thumb.jpg
5124594200_1615482995_thumb.jpg 5913176300_1615482997_thumb.jpg

Because most of the modifications need messing with the TIA pins, I am wondering if it would just be quickier to make an add-on board with DIL40 socket to put in pleace where TIA sits. That would require almost no modification on the original board and would be reversible.

 

Edited by krzysiobal
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Hello,

 

@krzysiobal : Amazing !That's very temptating but some steps looks a little bit complicated to my humble skills. Any update with your great idea of an add-board ? It would be sooooooooooo great and sooooooo much appreciated ! Thanks a lot +++

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